Be strong, not long till you can find out for yourself. I've seen the first episode, and it's shown, but not totally explained, roll on next week, mind you yet again I'll be tied to the television!
The hatch is a bunker of the Dharma initiative, with a clock which has to be reset every 108 minutes ( for some reason ) inside are weapons, a video, which you will see and all sorts of communication equipment. I will leave the rest for you to watch.
Inside is a man called desmond that jack met once. he was put in there for an experiement. he has to put in the 'numbers' every 108 minutes. he runs off and isn't seen for most of the season but i know that the season finale is a massive desmond flashback. also at the end of season you find out how the plane crashed... it wasn't an accident!